Laundry washing machines are used in many single-family and multi-family residential applications to clean clothes and other fabric items. During different phases of a wash cycle, a load of items will generally be subject to different operations that can introduce forces and/or vibrations not only to the load but also to the machine itself and/or to its surroundings. During a wash phase, for example, a wash tub may be filled with water and an agitator or impeller may be used to agitate the water and the load. During a rinse phase, a wash basket within the wash tub may be spun and/or the agitator/impeller may again be used to assist with rinsing detergent and soil from the load. In addition, during a spin phase, the wash basket is generally spun at a relatively high speed to extract water from the load.
Given that the contents of a wash tub, as well as the moving components within a laundry washing machine, have a mass, movement of these bodies can introduce undesirable forces, typically perceived as vibrations, not only to the fixed components of the machine but also to the floor or other surrounding structure in a dwelling. In addition, even within a given wash cycle, this mass can vary considerably as water is added to or removed from the wash tub.
In some laundry washing machine designs, a suspension system is used to attempt to isolate a floating or suspended portion of the machine (e.g., the wash tub and the movable and other force-generating components) from the non-suspended components (e.g., the cabinet or housing) and the surrounding environment, and thereby reduce the amount of forces and vibrations communicated to the non-suspended components and the surrounding environment. In a top load laundry washing machine, for example, a wash tub may be suspended on a set of support rods that are secured at one end to the cabinet or housing of the machine and secured at the other end to respective dampers secured in turn to the wash tub, e.g., proximate a bottom portion of the wash tub. The dampers may include springs and/or air or friction-based damping mechanisms, and through the suspension of the wash tub and the damping effect of the dampers, the forces and vibrations generated during a wash cycle can be substantially attenuated.
Nonetheless, the range of forces that may be generated during a wash cycle can vary considerably and can vary substantially even for different wash cycles due to differences in the sizes of the load and the amount of water used. Furthermore, excessive forces, e.g., due to out of balance loads, can overcome the damping effect of the suspension system and lead to undesirable levels of vibration as well as in some instances undesirable noises such as cabinet banging that result from excessive displacement of the suspended portion. As a result, many conventional washing machines make a number of tradeoffs, such as tuning suspension systems for “average” loads and limiting operations such as spinning the wash basket during the spin phase to speeds that are below the speeds that might otherwise be used for certain loads to ensure that excessive vibrations and/or noises are not encountered in other loads. Furthermore, it has been found that suspension systems can wear over time and as a result the damping effect of such systems can also change over time.